A MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor), such as a DMOSFET (Double Diffused MOSFET), or an IGBT (Insulated Gate Bipolar Transistor) is used as a switching element of an electronic circuit, such as a three-phase inverter circuit or an H bridge circuit. A gate drive signal is supplied to a gate terminal of the MOSFET or of the IGBT through a gate resistor.
FIG. 5 is a graph showing a relationship among gate resistance, switching loss (DMOS Eoff) caused when a DMOSFET is turned off, and surge voltage and showing a relationship among gate resistance, switching loss (IGBT Eoff) caused when an IGBT is turned off, and surge voltage.
In the IGBT, the gate resistance dependency of switching loss at the turn-off time is low. Additionally, in the IGBT, the amount of increase of the surge voltage is small with respect to an increase of the gate resistance. On the other hand, in the DMOSFET, the switching loss at the turn-off time can be made much smaller by reducing the gate resistance than in the IGBT. However, in the DMOSFET, if the gate resistance is reduced, the rate of change di/dt of a drain current at the turn-off time will become great, and therefore a great surge voltage will be generated.
As shown in FIG. 4, Patent Literature 1 discloses an arrangement in which, in a three-phase inverter circuit including six IGBTs, a snubber circuit is connected between a single DC input terminal P to which a collector of high-side IGBTs equivalent to three phases is connected and a single DC input terminal N to which an emitter of low-side IGBTs equivalent to three phases is connected, in order to restrain a surge voltage.